Prior art of U.S. Pat. No. 4,812,231, owned by this assignee, has resulted in improvement of removing solid particles from a liquid influent by providing a cost effective apparatus, utilizing a rotating filter assembly with a flushing device mounted so as to discharge the debris that accumulates, greatly decreasing the need for manpower with respect to cleaning and removal of the unwanted particles. U.S. Pat. No. 5,102,536, an improvement over the rotating filter assembly, further improved the removal of solid particles from liquid influents by utilizing a projecting foot on link members mounted on the rotating filter so as to complete the break up of solids, such as fecal matter, that were not always broken up and discharged by the prior art assemblies. Further prior art of U.S. Pat. No. 6,177,020 and U.S. Pat. No. 6,669,854, also owned by this assignee, describes an alternative means of filtering waste streams containing solids by the use of a stepping screen assembly with a grid structure of bars. Multiple parallel alternate static and dynamic bars are driven by a pneumatic cylinder, lifting solids out of a liquid waste stream. Each bar has multiple vertically spaced apart shelves at a right angle to the vertical axis of the bar. The solid material moves upwards and over the top of the grid structure to fall by gravity onto a conveyor for delivery of the solids to a waste receptacle while the liquid moves through the grid structure without impediment.
Though these inventions provide an improvement over prior filtering methods, unwanted particles such as pine needles, textile threads, hair, seeds and other similarly sized debris are not removed using the present methods found in the prior art. These miniscule particles fall back into the filtered liquid influent. The mesh screens found in current filter assemblies cannot be supported if the openings are less than two millimeters in diameter. Miniscule particles such as pine needles, textile threads, hair or seeds are, therefore, not filtered by current screen assemblies. In addition, the assemblies for collection and discharge of large sized debris cannot be used for removal of smaller particles and vice versa, as the filter grids are not easily interchangeable. An improvement is needed that will support grids with smaller openings, allowing removal of these smaller unwanted particles in an efficient and cost effective manner, while still allowing interchangeability of filter grids to allow for easy maintenance and variation in the grid opening size within the same apparatus.